Cross-stream heat exchanger

ABSTRACT

A heat exchanger system for a gas turbine engine is disclosed. The heat exchanger system may include a first structure at least partially defining a first plenum configured to receive a first air stream, a second structure at least partially defining a second plenum configured to receive a second air stream having lower pressure than the first air stream, a third structure at least partially defining a third plenum configured to receive a third air stream having lower pressure than the second air stream, and a heat exchanger configured for operative communication with the first air stream, the second air stream, and the third air stream while disposed between the second air stream and the third air stream. The heat exchanger may be configured to transfer heat from the first air stream to the third air stream.

CROSS REFERENCE TO RELATED APPLICATIONS

This application a continuation application of patent application Ser.No. 15/109,183 filed Jun. 30, 2016 and claims priority to PatentApplication PCT/US2014/059220 filed on Oct. 6, 2014 and U.S. ProvisionalPatent Application No. 61/924,588, filed Jan. 7, 2014, the contents eachof which are incorporated herein by reference in their entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to gas turbine engines and,more particularly, to heat exchanger systems for gas turbine engines.

BACKGROUND OF THE DISCLOSURE

Gas turbine engines may typically include a fan, a compressor, acombustor, and a turbine, with an annular flow path extending axiallythrough each. Initially, the fan, which is powered by the turbine, drawsambient air into the engine. Part of the air flows through thecompressor where it is compressed or pressurized. The combustor thenmixes and ignites the compressed air with fuel, generating hotcombustion gases. These hot combustion gases are then directed from thecombustor to the turbine where power is extracted from the hot gases bycausing blades of the turbine to rotate. This flow path may be referredto as a core flow path. The other part of the airflow from the fan,which may be referred to as a bypass flow path, is used to generateforward thrust.

Gas turbine engines operate at extremely high temperatures. Thesetemperatures may exceed the temperature limits of some of the materialsof the engine components. Therefore, cooling air may be supplied to theengine components in order to cool the hot components. For example,cooling air may be extracted from the compressor section and directed tocertain components of the turbine section.

Furthermore, in some cases, the cooling air extracted from thecompressor section may have to be further cooled by fan air from thebypass flow path before being delivered to the turbine components. Thisair may be referred to as cooled cooling air (CCA). CCA may be suppliedcontinuously throughout engine operation. However, there may besituations when CCA is not required, which results in pressure loss fora specific thrust requirement, thereby reducing fuel burn.

Accordingly, there exists a need for a system and method that adequatelyprovides CCA to turbine components while minimizing pressure loss.

SUMMARY OF THE DISCLOSURE

According to one embodiment of the present disclosure, a heat exchangersystem for a gas turbine engine is disclosed. The heat exchanger systemmay comprise a first structure at least partially defining a firstplenum configured to receive a first air stream, a second structure atleast partially defining a second plenum configured to receive a secondair stream having lower pressure than the first air stream, a thirdstructure at least partially defining a third plenum configured toreceive a third air stream having lower pressure than the second airstream, and a heat exchanger configured for operative communication withthe first air stream, the second air stream, and the third air streamwhile disposed between the second air stream and the third air stream.The heat exchanger may be configured to transfer heat from the first airstream to the third air stream.

In a refinement, the heat exchanger may be disposed within a second ductsurrounding the second air stream, the second duct including aerodynamicsurfaces surrounding the heat exchanger.

In another refinement, the first air stream may comprise a core flowpath, and each of the second air stream and the third air stream may becomprised of a bypass flow path.

In another refinement, the heat exchanger may include: a first inletassociated with the first air stream, a first exit associated with acooling air, a plurality of first passages extending from the firstinlet to the first exit, a second inlet associated with the second airstream, a second exit associated with the third air stream, and aplurality of second passages extending from the second inlet to thesecond exit. A portion of the first air stream may flow into the firstinlet through the plurality of first passages and out of the first exit.A portion of the second air stream may flow into the second inletthrough the plurality of second passages and out of the second exit. Theheat exchanger may transfer heat between the portion of the first airstream in the plurality of first passages and the portion of the secondair stream in the plurality of second passages.

In another refinement, the cooling air exiting from the first exit ofthe heat exchanger may be used to cool components of the gas turbineengine.

In another refinement, the heat exchanger may include a scoop designedto capture air flow.

In another refinement, the heat exchanger may include a flow meteringdevice configured to control flow through the heat exchanger.

In another refinement, the flow metering device may be positionedproximate a forward side of the heat exchanger.

In another refinement, the flow metering device may be positionedproximate an aft side of the heat exchanger.

In another refinement, the flow metering device may be positionedproximate an inlet or an exit of the heat exchanger.

According to another embodiment of the present disclosure, a method forcooling components of a gas turbine engine is disclosed. The method maycomprise installing a heat exchanger between two air streams havingdifferent air pressures, using the heat exchanger to cool air from acore flow path of the gas turbine engine, and supplying the cooled airfrom the heat exchanger to components of the gas turbine engine.

In a refinement, the method may further comprise providing the heatexchanger with a flow metering device configured to modulate flowthrough the heat exchanger.

In another refinement, the method may further comprise selectivelyallowing flow through the heat exchanger using the flow metering device.

In another refinement, the method may further comprise opening the flowmetering device to allow flow through the heat exchanger when coolingair is required.

In another refinement, the method may further comprise closing the flowmetering device to stop flow through the heat exchanger when cooling airis not required.

In another refinement, the method may further comprise providing theflow metering device proximate an inlet or an exit of the heatexchanger.

According to yet another embodiment of the present disclosure, a gasturbine engine is disclosed. The gas turbine engine may comprise a firstair duct surrounding a first air stream, a second air duct surrounding asecond air stream, a third air duct surrounding a third air stream, anda heat exchanger disposed within the second air duct. The second airstream may surround the first air duct and have a lower pressure thanthe first air stream. The third air stream may surround the second airduct and have a lower pressure than the second air stream.

In a refinement, air flow from a combustor may mix with a cooling airfrom the heat exchanger for delivery to hot components.

In another refinement, the second air duct may include fairing memberssurrounding the heat exchanger.

In another refinement, the heat exchanger may include an integratedscoop and flow metering device to capture and modulate air flow.

These and other aspects and features of the disclosure will become morereadily apparent upon reading the following detailed description whentaken in conjunction with the accompanying drawings. Although variousfeatures are disclosed in relation to specific exemplary embodiments ofthe invention, it is understood that the various features may becombined with each other, or used alone, with any of the variousexemplary embodiments of the invention without departing from the scopeof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side, partially cross-sectional view of a gas turbineengine, in accordance with the present disclosure;

FIG. 2 is a cross-sectional view of a heat exchanger system installed inthe gas turbine engine of FIG. 1, according to an embodiment of thepresent disclosure;

FIG. 3 is a cross-sectional view of a flow metering device positionednear a forward side of the heat exchanger system of FIG. 2, according toanother embodiment of the present disclosure;

FIG. 4 is a perspective view of an integrated scoop and flow meteringdevice, according to another embodiment of the present disclosure;

FIG. 5 is a cross-sectional view of a flow metering device positionednear an aft side of the heat exchanger system of FIG. 2, according toanother embodiment of the present disclosure;

FIG. 6 is a cross-sectional view of a flow metering device positioned onan inlet of the heat exchanger system of FIG. 2, according to anotherembodiment of the present disclosure;

FIG. 7 is a cross-sectional view of a flow metering device positioned onan exit of the heat exchanger system of FIG. 2, according to anotherembodiment of the present disclosure;

FIG. 8 is a cross-sectional view of a flow metering device positioned onanother exit of the heat exchanger system of FIG. 2, according toanother embodiment of the present disclosure; and

FIG. 9 is a flowchart outlining a process for cooling components of agas turbine engine, according to yet another embodiment of the presentdisclosure.

While the present disclosure is susceptible to various modifications andalternative constructions, certain illustrative embodiments thereof,will be shown and described below in detail. It should be understood,however, that there is no intention to be limited to the specificembodiments disclosed, but on the contrary, the intention is to coverall modifications, alternative constructions, and equivalents fallingwithin the spirit and scope of the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, and with specific reference to FIG. 1, inaccordance with the teachings of the disclosure, an exemplary gasturbine engine 20 is shown. The gas turbine engine 20 may generallycomprise a fan section 22 which draws ambient air into the engine 20, acompressor section 24 where part of the air flow from the fan section ispressurized, a combustor section 26 downstream of the compressor sectionwhich mixes and ignites the compressed air with fuel and therebygenerates hot combustion gases, a turbine section 28 downstream of thecombustor section 26 for extracting power from the hot combustion gases,and a first air stream 30 extending axially through each. The other partof the air flow from the fan section 22 may comprise a bypass flow path32 used to generate forward thrust.

Gas turbine engine 20 may be used on an aircraft for generating thrustor power, or in land-based operations for generating power as well. Itis understood that gas turbine engine 20 may include fewer or additionalsections than fan section 22, compressor section 24, combustor section26, and turbine section 28.

The first air stream 30 may flow along an annular core flow path of thegas turbine engine. An engine casing or first air duct 34 may enclosecompressor section 24, combustor section 26, turbine section 28, andfirst air stream 30. Generally, the fan section 22 may drive air alongthe bypass flow path 32, and the compressor section 24 may drive airalong the core flow path or first air stream 30.

Referring now to FIG. 2, with continued reference to FIG. 1, a firstplenum 29 may be configured to receive the first air stream 30, a secondplenum 35 may be configured to receive a second air stream 36, and athird plenum 39 may be configured to receive a third air stream 40within the gas turbine engine 20. Structures 27 may at least partiallydefine the first plenum 29. Structures 33 may at least partially definethe second plenum 35, and structures 37 may at least partially definethe third plenum 39.

The second air stream 36 may surround the first air duct 34, and asecond air duct 38 may enclose the second air stream 36. The third airstream 40 may surround the second air duct 38, and a third air duct 42may enclose the third air stream 40. Each of the second air stream 36and the third air stream 40 may be comprised of bypass flow paths fromthe fan section 22, e.g., a first fan stream and a second fan stream.The first air stream 30 may have a higher air pressure/temperature thanthe second air stream 36, and the second air stream 36 may have a higherair pressure/temperature than the third air stream 40.

A heat exchanger system 44 may be installed in the gas turbine engine 20in order to supply cooled cooling air (CCA) to engine components.According to an embodiment of the present disclosure, the heat exchangersystem 44 may comprise a heat exchanger 46 positioned between the secondair stream 36 and the third air stream 40. For example, heat exchanger46 may be disposed within the second air duct 38. Aerodynamic contouringmay be applied to the heat exchanger system 44 in order to minimizepressure loss. For instance, the second air duct 38 may includeaerodynamic surfaces 48 surrounding the heat exchanger 46. Aerodynamicsurfaces 48 may comprise fairings designed to increase streamlining andreduce drag around the heat exchanger system 44. It is to be understoodthat the gas turbine engine 20 may include a plurality of heat exchangersystems 44 and a plurality of heat exchangers 46.

In operative communication with the first air stream 30, the second airstream 36, and the third air stream 40, heat exchanger 46 may beconfigured to transfer heat from one air stream to another in order toprovide CCA to hot components of the gas turbine engine 20. For example,heat exchanger 46 may comprise a plate heat exchanger, although othertypes of heat exchangers are certainly possible. Heat exchanger 46 mayinclude a first inlet 50 associated with the first air stream 30, asecond inlet 52 associated with the second air stream 36, a first exit54 associated with a cooling air or CCA 56, and a second exit 58associated with the third air stream 40. The inlets 50, 52 and exits 54,58 may comprise openings, apertures, pipes, tubes, or any otherstructure which provides communication of the heat exchanger 46 with thedifferent air streams 30, 36, 40. A plurality of first parallel flowpassages 60 may extend from the first inlet 50 to the first exit 54, anda plurality of second parallel flow passages 62 may extend from thesecond inlet 52 to the second exit 58.

A portion 64 of the first air stream 30 may be extracted from thecompressor section 24, such as, from a low or high compressor, in orderto be cooled for the supply of CCA to hot components of the gas turbineengine 20. Since the second air stream 36 has a lower temperature thanthe first air stream 30, a portion 66 of the second air stream 36 may beused to cool the portion 64 of the first air stream 30 via heatexchanger 46. The portion 64 of the first air stream 30 enters the firstinlet 50 and flows through the plurality of first passages 60 of theheat exchanger 46, while the portion 66 of the second air stream 36enters the second inlet 52 and flows through the plurality of secondpassages 62 of the heat exchanger 46. While flowing through theplurality of first and second passages 60, 62 of the heat exchanger 46,heat is transferred from the portion 64 of the first air stream 30 tothe portion of 66 of the second air stream 36.

Due to the heat transfer via heat exchanger 46, the portion 64 of thefirst air stream 30 is cooled and comprises the CCA 56, which flows outof the first exit 54 and onto the components of the gas turbine engine20 that need cooling. For example, CCA 56 may be directed to thecompressor section 24 and the turbine section 28, such as to blades 68and rim cavities 70 of a high pressure compressor 72 and/or a highpressure turbine 74. CCA 56 may certainly be used to cool blades and rimcavities of a low pressure compressor and/or a low pressure turbine, andother hot components of the gas turbine engine 20 as well. Furthermore,air flow 76 from a combustor 78 of the gas turbine engine 20 may be usedto mix with the CCA 56 from the heat exchanger 46 in order to increaseair pressure of the CCA 56 for delivery to the hot components (e.g.,blades 68 and rim cavities 70).

In addition, since the second air stream 36 has a higher pressure thanthe third air stream 40, the portion 66 of the second air stream 36(which has a higher temperature after heat transfer via heat exchanger46) flows out of the second exit 58 and into the third air stream 40.Therefore, heat from the portion 64 of the first air stream 30 isultimately transferred to the third air stream 40. Since the heatexchanger 46 is located between the second air stream 36 and the thirdair stream 40, the pressure difference between the second and third airstreams 36, 40, provides efficient flow of the portion 66 of the secondair stream 36 into the third air stream 40. It is to be understood thatalthough shown and described as being positioned between the second airstream 36 and the third air stream 40, heat exchanger 46 may bepositioned between any two air streams which have a pressure differencerelative to each other.

Turning now to FIG. 3, with continued reference to FIGS. 1 and 2, theheat exchanger system 44 may further include a flow metering device 80.The flow metering device 80 may be configured to control flow throughthe heat exchanger 46. For example, when cooling or CCA is requiredduring engine operation, the flow metering device 80 may allow flow(e.g. portions 64 of the first air stream 30, portion 66 of the secondair stream 36, and CCA 56) through the heat exchanger 46. When coolingor CCA is not required, the flow metering device 80 may actuate to stopflow through the heat exchanger 46, thereby reducing pressure lossincurred via flow through the heat exchanger 46. In addition, the flowmetering device 80 may have an aerodynamic design or shape configured toreduce pressure loss.

The flow metering device 80 may comprise, without limitation, a door, avalve, a butterfly valve, a gate valve, check valve, or any othermodulating device that can regulate flow through the heat exchanger 46.For example, as shown best in FIG. 4, the flow metering device 80 maycomprise a plurality of slats 82 in a louver style arrangement. It is tobe understood that although the slats 82 are oriented horizontally inFIG. 4, they may be arranged in a vertical or angled orientation aswell. Furthermore, the flow metering device 80 may have a low pressureloss design in order to maximize the pressure available to the heatexchanger 46. The flow metering device 80 may have an on or openposition to allow flow through the heat exchanger 46 and an off orclosed position to stop flow through the heat exchanger 46. In addition,the flow metering device 80 may have positions between fully open andfully closed in order to modify the amount of flow through the heatexchanger 46, such as, depending on specific CCA requirements.

Various methods may be used to the flow metering device 80. For example,a sensor may be used to measure a pressure and/or temperature flow, orother condition, and the flow metering device 80 may be actuated toreach a certain set point or position based on the sensor feedback ofthe measured condition. The flow metering device 80 may also beindependent of sensor feedback and may be actuated based on a setpredetermined schedule, such as, based on flight conditions. In anotherexample, the flow metering device 80 may be in communication with acontroller, which may manage the flow metering device 80 according to ahigh fidelity control. The flow metering device 80 may be purely drivenby the pressure difference between the second and third air streams 36,40 such that the flow metering device 80 opens as the pressuredifference increases and closes as the pressure difference decreases. Inyet another example, the flow metering device 80 may comprise a complexflow control device having aerodynamic bearings and a variety of flowmetering devices controlled by an engine computer controller.

As shown in FIG. 3, the flow metering device 80 may be positioned at afront or forward side 84 of the heat exchanger 46. For example, the flowmetering device 80 may be located on the second inlet 52 associated withthe portion 66 of the second air stream 36. In another example, shownbest in FIG. 5, the flow metering device 80 may be positioned at a rearor aft side 86 of the heat exchanger 46. As shown in FIG. 6, the flowmetering device 80 may be located on the first inlet 50 associated withthe portion 64 of the first air stream 30. As shown in FIG. 7, the flowmetering device 80 may also be located on the first exit 54 associatedwith the CCA 56. As shown in FIG. 8, the flow metering device 80 may belocated on the second exit 58 associated with the third air stream 40,as well.

It is to be understood that the flow metering device 80 may also bepositioned in other locations than that shown and described.Furthermore, the heat exchanger system 44 may have more than one flowmetering device 80 or no flow metering device 80 at all. For example, afirst flow metering device may be positioned on the forward side 84 ofthe heat exchanger 46 and a second flow metering device may bepositioned on the aft side 86 of the heat exchanger 46, such as, on anyof the inlets 50, 52 and/or exits 54, 58.

Furthermore, the heat exchanger system 44 may include a scoop 88integrated into the flow metering device 80, as shown best in FIG. 4.The scoop 88 may be designed to capture and direct maximum air flow intothe heat exchanger 46 at an elevated pressure. In so doing, the scoop 88minimizes pressure loss and reduces exit temperatures of the heatexchanger 46. The integrated scoop 88 and flow metering device 80enables flow capture and modulation of flow. It is to be understood thatthe scoop 88 may not be integrated with the flow metering device 80, andthat the heat exchanger system 44 may have a separate scoop 88 inaddition to the flow metering device(s) 80.

Referring now to FIG. 9, with continued reference to FIGS. 1-8, aflowchart outlining a process 90 for cooling components of the gasturbine engine 20 is shown, according to another embodiment of thepresent disclosure. At a block 92, the heat exchanger 46 may beinstalled between two air streams 36, 40 having different air pressures.At a block 94, the heat exchanger 46 may be used to cool air 64 from acore flow path 30 of the gas turbine engine 20. The cooled air or CCA 56from the heat exchanger 46 may be supplied to components of the gasturbine engine 20.

INDUSTRIAL APPLICABILITY

From the foregoing, it can be seen that the teachings of this disclosurecan find industrial application in any number of different situations,including but not limited to, gas turbine engines. Such engines may beused, for example, on aircraft for generating thrust, or in land,marine, or aircraft applications for generating power.

The present disclosure provides a heat exchanger system and process forcooling components of the gas turbine engine. In the disclosed systemand method, the heat exchanger is installed in an aerodynamicallycontoured area between (cross-stream) two bypass air streams around theengine core. The pressure difference between the two bypass air streamsprovides a cold side flow, which is used to cool air from the enginecore.

Furthermore, the flow metering device of the present disclosure maymodulate flow between the two air streams depending on the coolingrequirements. The flow metering device at the front of the heatexchanger is a simplified, low cost solution. Moreover, the integratedscoop increases flow through the heat exchanger, thereby minimizingpressure loss and reducing a cold side exit temperature. Positioning theflow metering device at the rear of the heat exchanger (e.g., CCA or hotside exit) may provide a desirable lower pressure and/or separatedexhaust, while positioning the flow metering device on the engine coreair stream (hot side) inlet may minimize pipe volume and protect theheat exchanger from large temperature excursions.

Compared to prior art heat exchangers which were typically installedin-line with an air stream flow, the aerodynamic contouring applied tothe installed cross-stream heat exchanger incurs a smaller amount ofpressure loss. In addition, since cooling is not required across theentire mission profile, the disclosed heat exchanger system with a flowmetering device allows reduced pressure loss for a specific thrustrequirement, which results in reduced fuel burn.

While the foregoing detailed description has been given and providedwith respect to certain specific embodiments, it is to be understoodthat the scope of the disclosure should not be limited to suchembodiments, but that the same are provided simply for enablement andbest mode purposes. The breadth and spirit of the present disclosure isbroader than the embodiments specifically disclosed, but rather includesall embodiments and equivalents encompassed within the claims appendedhereto as well.

What is claimed is:
 1. A heat exchanger system for a gas turbine engine,comprising: a first structure at least partially defining a first plenumconfigured to receive a first air stream; a second structure at leastpartially defining a second plenum configured to receive a second airstream having lower pressure than the first air stream; a thirdstructure at least partially defining a third plenum configured toreceive a third air stream having lower pressure than the second airstream; and a heat exchanger configured for operative communication withthe first air stream, the second air stream, and the third air stream,the heat exchanger configured to transfer heat from a portion of thefirst air stream to a portion of the second air stream at the heatexchanger, the portion of the second air stream flowing to the third airstream, the heat exchanger disposed between the second structure and thethird structure; wherein the heat exchanger includes a flow meteringdevice configured to control flow through the heat exchanger, the flowmetering device including a plurality of slats in a louver arrangement.2. The heat exchanger system of claim 1, wherein the heat exchanger isdisposed within a second duct surrounding the second air stream, thesecond duct including aerodynamic surfaces surrounding the heatexchanger.
 3. The heat exchanger system of claim 1, wherein the firstair stream comprises a core flow path, and each of the second air streamand the third air stream is comprised of a bypass flow path.
 4. The heatexchanger system of claim 1, wherein the heat exchanger includes: afirst inlet associated with the first air stream, a first exitassociated with a cooling air, a plurality of first passages extendingfrom the first inlet to the first exit, a second inlet associated withthe second air stream, a second exit associated with the third airstream, and a plurality of second passages extending from the secondinlet to the second exit, wherein a portion of the first air streamflows into the first inlet, through the plurality of first passages andout of the first exit, wherein a portion of the second air stream flowsinto the second inlet through the plurality of second passages and outof the second exit, and wherein the heat exchanger transfers heatbetween the portion of the first air stream in the plurality of firstpassages and the portion of the second air stream in the plurality ofsecond passages.
 5. The heat exchanger system of claim 4, wherein thecooling air exiting from the first exit of the heat exchanger is used tocool components of the gas turbine engine.
 6. The heat exchanger systemof claim 1, wherein the heat exchanger includes a scoop designed tocapture air flow.
 7. The heat exchanger system of claim 1, wherein theflow metering device is positioned proximate a forward side of the heatexchanger.
 8. The heat exchanger system of claim 1, wherein the flowmetering device is positioned proximate an aft side of the heatexchanger.
 9. The heat exchanger system of claim 1, wherein the flowmetering device is positioned proximate an inlet or an exit of the heatexchanger.
 10. The heat exchanger system of claim 1, wherein the flowmetering device has one or more positions between a fully openedposition and a fully closed position.
 11. A method for coolingcomponents of a gas turbine engine, the method comprising: providing afirst structure at least partially defining a first plenum configured toreceive a first airflow; providing a second structure at least partiallydefining a second plenum configured to receive a second airflow having alower pressure than the first airflow; providing a third structure atleast partially defining a third plenum configured to receive a thirdairflow having lower pressure than the second airflow; installing a heatexchanger between the second structure and the third structure, usingthe heat exchanger to transfer heat from a portion of the first airflowto a portion of the second airflow at the heat exchanger, the firstairflow originating from a core flow path of the gas turbine engine; andsupplying a portion of the second airflow to the third airflow; whereinthe heat exchanger includes a flow metering device configured to controlflow through the heat exchanger, the flow metering device including aplurality of slats in a louver arrangement.
 12. The method of claim 11,further comprising selectively allowing flow through the heat exchangerusing the flow metering device.
 13. The method of claim 12, furthercomprising opening the flow metering device to allow flow through theheat exchanger when cooled first airflow is required.
 14. The method ofclaim 13, further comprising closing the flow metering device to stopflow through the heat exchanger when cooled first airflow is notrequired.
 15. The method of claim 11, further comprising providing theflow metering device proximate an inlet or an exit of the heatexchanger.
 16. A gas turbine engine comprising: a first air ductsurrounding a first air stream; a second air duct surrounding a secondair stream, the second air stream surrounding the first air duct andhaving a lower pressure than the first air stream; a third air ductsurrounding a third air stream, the third air stream surrounding thesecond air duct and having a lower pressure than the second air stream;and a heat exchanger disposed between the second air duct and the thirdair duct, the heat exchanger configured to exchange thermal energybetween the first airstream and the second air stream; wherein the heatexchanger includes a flow metering device configured to control flowthrough the heat exchanger, the flow metering device including aplurality of slats in a louver arrangement.
 17. The gas turbine engineof claim 16, wherein air flow from a combustor mixes with a cooling airfrom the heat exchanger for delivery to hot components.
 18. The gasturbine engine of claim 17, wherein the second air duct includesfairings surrounding the heat exchanger.
 19. The gas turbine engine ofclaim 17, wherein the heat exchanger includes an integrated scoop tocapture and modulate air flow.
 20. The gas turbine engine of claim 17,wherein the flow metering device has one or more positions between afully opened position and a fully closed position.